Go to Edit Page of your wanted page and scroll down: there will be an area labelled as "Discussion" where you can choose to allow comments and also pingbacks and trackbacks. Uncheck it/them, update page, repeat the process for the other pages you want and that should do it.
Follow this method if you also want no comments on some posts - this time by going to Edit Post instead of Edit Page. There's also an option on your dashboard menu -> Settings -> Discussion section where you can choose to allow people to post comments on new articles or not by default (these settings may be overridden for individual articles.)
Here are the support pages: http://en.support.wordpress.com/pages/new-page-screen/#discussion, http://en.support.wordpress.com/posts/new-post-screen/#discussion

In fact, there's an easier way to enable/disable comments on multiple pages simultaneously: go on your dashboard menu -> Pages, check the pages you want, go on the "Bulk Actions" dropdown menu at the top, select "Edit" and click "Apply. A new section will appear: click on the dropdown menu labelled as "Comments", choose "Do not allow" and update. The method for enabling/disabling comments on posts is the same, you'll just have to go to the Posts section instead of Pages.